1. Field of the Invention
This invention relates to valves used to close the interior of a conduit, such as a tubing string, and the annular area between a tubing string and an exterior casing in a subterranean well.
2. Description of the Prior Art
In subterranean wells, especially offshore wells, it is necessary to provide a means of closing off the tubing string and the annular area between the tubing and the casing to prevent produced fluids from being ejected from the well in case of damage to the well head. In conventional use of safety valves for controlling the flow of fluid in the tubing or in the annulus, these safety valves are mounted in a hanger secured to the outer casing and supporting the tubing extending below the hanger. An example of one single string tubing hanger is shown on pages 760 and 761 of the 1980-81 Composite Catalog of Oil Field Equipment and Services published by World Oil. Some prior art hangers also employ an exterior packoff member for establishing a seal between the hanger and the external casing. For example, one prior art hanger employs a single grip anchoring device in which radially expandable slips hold the hanger secured to the exterior casing and support the weight of the tubing. The packoff member is acted upon by the weight of the tubing and by the inner directional slip system to maintain a compressive load upon the packoff member, thus maintaining a suitable annular seal.
If a single string completion is employed and if it is necessary to inject a treating fluid from the surface while producing through the single string completion, then production must occur in either the tubing or the tubing casing annulus while injection takes place through the other passage. In such a system it is then necessary to employ not only a safety valve to close the single tubing string, but also to use a annulus safety valve to close that alternate passage. Any of a number of safety valves for controlling the flow in the tubing string may be employed in those completions where control in both the tubing and in the annulus are necessary. These tubing safety valves can be either a ball type or flapper type safety valve, and conventionally these valves would be controlled by the injection of fluid through an exterior control line extending to the surface of the well. By pressurizing the valve through the control fluid string the flapper may be opened to permit flow in the tubing. When pressure is removed, either intentionally or by virtue of an accident at the well head, these spring biased ball or flapper valves will close to shut off flow from the tubing. In addition to safety valves for controlling the flow through the tubing string, some means must be provided for controlling the flow from the annulus. Annulus safety valves mounted in the hanger and employing valves for opening and closing a bypass around a hanger packoff member are known in the prior art.